Elliott Brothers

 Elliott 503 console for the first prototype 503 machine, late 1962/early 1963.

 First prototype of the Elliott 503 computer by Elliott Brothers, late 1962/early 1963.

 Jack Smith (Elliott Brothers) testing a board on the prototype 503, late 1962/early 1963.

Additional interpretive comments from Brian Marriott about this picture: 

The machine he's working on is a basic machine. No Core Backing Store or other peripheral cabinet.

The cabinets visible with the doors open are: on his left the Store, in the middle the CPU and on his right the Power Supply.

Where Jack is working on the machine, he has all the doors off the cabinets. Those cabinets had hinged doors for normal access, but you could lift them off their hinges when you needed full access; we usually only did that on a full maintenance shutdown.

Jack has one of the CPU boards out on an extender ("stalk") board - giving full access to its circuitry while allowing it to connect properly to the back wiring. (I was about to say "backplane" but it was all sockets & soldered wires.) There were times when we had a connector-related or thermal intermittent fault when we'd run a board on the stalk for some days, waiting for the fault to re-occur.

The cabling loom visible in the CPU cabinet behind Jack was the wiring that served the display panel. As can be seen on the attached CPU board pic, the boards had connectors on both ends - the primary connector fitted into the rack-mounted socket; the secondary connector received a floating socket on the other side of the cabinet.